Airway epithelial damage and release of inflammatory mediators in human lung parenchyma after sulfur mustard exposure

Identification of early events in nitrogen mustard pulmonary toxicity that are independent of infiltrating inflammatory cells using precision cut lung slices

Nitrogen mustard (NM; mechlorethamine) is a cytotoxic vesicant known to cause acute lung injury which can progress to chronic disease. Due to the complex nature of NM injury, it has been difficult to analyze early responses of resident lung cells that initiate inflammation and disease progression. To investigate this, we developed a model of acute NM toxicity using murine precision cut lung slices (PCLS), which contain all resident lung cell populations. PCLS were exposed to NM (1-100 μM) for 0.5-3 h and analyzed 1 and 3 d later. NM caused a dose-dependent increase in cytotoxicity and a reduction in metabolic activity, as measured by LDH release and WST-1 activity, respectively. Optimal responses were observed with 50 μM NM after 1 h incubation and these conditions were used in further experiments. Analysis of PCLS bioenergetics using an Agilent Seahorse showed that NM impaired both glycolytic activity and mitochondrial respiration. This was associated with injury to the bronchial epithelium and a reduction in methacholine-induced airway contraction. NM was also found to cause DNA damage in bronchial epithelial cells in PCLS, as measured by expression of γ-H2AX, and to induce oxidative stress, which was evident by a reduction in glutathione levels and upregulation of the antioxidant enzyme catalase. Cleaved caspase-3 was also upregulated in airway smooth muscle cells indicating apoptotic cell death. Characterizing early events in NM toxicity is key in identifying therapeutic targets for the development of efficacious countermeasures.

Free Radical Production and Oxidative Stress in Lung Tissue of Patients Exposed to Sulfur Mustard: An Overview of Cellular and Molecular Mechanisms

Sulfur mustard (SM) is a chemical alkylating compound that primary targets lung tissue. It causes a wide variety of pathological effects in respiratory system such as chronic bronchitis, bronchiolitis obliterans, necrosis of the mucosa and inflammation, chronic obstructive pulmonary disease (COPD), and pulmonary fibrosis. However, molecular and cellular mechanisms for these pathologies are still unclear. Oxidative stress (OS) induced by reactive oxygen species (ROS) is likely a significant mechanism by which SM leads to cell death and tissues injury. SM can trigger various molecular and cellular pathways that are linked to ROS generation, OS, and inflammation. Hypoxia-induced oxidative stress, reduced activity of enzymatic antioxidants, depletion of intercellular glutathione (GSH), decreased productivity of GSH-dependent antioxidants, mitochondrial dysfunction, accumulation of leukocytes and proinflammatory cytokines, and increased expression of ROS producing-related enzymes and inflammatory mediators are the major events in which SM leads to massive production of ROS and OS in pulmonary system. Therefore, understanding of these molecules and signaling pathways gives us valuable information about toxicological effects of SM on injured tissues and the way for developing a suitable clinical treatment. In this review, we aim to discuss the possible mechanisms by which SM induces excessive production of ROS, OS, and antioxidants depletion in lung tissue of exposed patients.

Altered expression of cyclooxygenase-2, 12-lipoxygenase, inducible nitric oxide synthase-2 and surfactant protein D in lungs of patients with pulmonary injury caused by sulfur mustard

CONTEXT

Sulfur mustard (SM) is a strong alkylating toxicant that targets different organs, particularly human lung tissue. Change in genes expression is one of the molecular mechanisms of SM toxicity in damaged tissue.

OBJECTIVE

The purpose of this investigation is to characterize the expression of cyclooxygenase-2 (COX-2), 12-lipoxygenase (12-LO), inducible nitric oxide synthase 2 (iNOS2), and surfactant protein D (SFTPD) in lungs of patients who exposed to SM.

METHODS

Lung biopsies were provided from SM-exposed patients (n = 6) and controls (n = 5). Total RNA were extracted from all specimens and then cDNA was synthesized for each sample. Changes in gene expression were measured using RT² Profiler ™PCR Array.

RESULTS

Pulmonary function tests revealed more obstructive and restrictive spirometric patterns among patients compared to the control group. Expression of COX-2 and 12-LO in the lung of patients was increased by 6.2555 (p = 0.004) and 6.2379-folds (p = 0.002), respectively. In contrast, expression of SF-D and iNOS genes was reduced by 8.5869-fold (p = 0.005) and 2.4466-folds (p = 0.011), respectively.

CONCLUSIONS

Mustard lungs were associated with overexpression of COX-2 and 12-LO, which are responsible for inflammation, overproduction of free radicals and oxidative stress. Downregulation of iNOS2 and SF-D are probably the reason for lung disease and dysfunction among these patients. Therefore, the expression of these genes could be an important, routine part of the management of such patients.

Mustard vesicant-induced lung injury: Advances in therapy

Most mortality and morbidity following exposure to vesicants such as sulfur mustard is due to pulmonary toxicity. Acute injury is characterized by epithelial detachment and necrosis in the pharynx, trachea and bronchioles, while long-term consequences include fibrosis and, in some instances, cancer. Current therapies to treat mustard poisoning are primarily palliative and do not target underlying pathophysiologic mechanisms. New knowledge about vesicant-induced pulmonary disease pathogenesis has led to the identification of potentially efficacious strategies to reduce injury by targeting inflammatory cells and mediators including reactive oxygen and nitrogen species, proteases and proinflammatory/cytotoxic cytokines. Therapeutics under investigation include corticosteroids, N-acetyl cysteine, which has both mucolytic and antioxidant properties, inducible nitric oxide synthase inhibitors, liposomes containing superoxide dismutase, catalase, and/or tocopherols, protease inhibitors, and cytokine antagonists such as anti-tumor necrosis factor (TNF)-α antibody and pentoxifylline. Antifibrotic and fibrinolytic treatments may also prove beneficial in ameliorating airway obstruction and lung remodeling. More speculative approaches include inhibitors of transient receptor potential channels, which regulate pulmonary epithelial cell membrane permeability, non-coding RNAs and mesenchymal stem cells. As mustards represent high priority chemical threat agents, identification of effective therapeutics for mitigating toxicity is highly significant.

A case control study of cardiovascular health in chemical war disabled Iranian victims

Background:

Sulfur mustard (SM) is an alkylating chemical warfare agent that was widely used during Iran–Iraq war between 1983 and 1988. SM exposure leads to various late complications. The aim of this study was to determine the late cardiovascular effects of SM in war-disabled Iranian victims.

Materials and Methods:

This was a retrospective cohort case control study on 50 patients with symptoms of SM exposure and 50 cases who had been in Iran–Iraq war, without chemical injury. We performed exercise stress test and echocardiography for all of patients.

Results:

The study group comprised 100 males of mean age 45.6 ± 6.2 years. In chemical war injury group, two patients (4%) had positive exercise stress test. On coronary angiography, they were found to have coronary artery disease. One patient had severe mitral regurgitation and normal coronary angiography; he was referred for mitral valve replacement. Left ventricular (LV) diastolic abnormality was detected in 23% of these subjects. In another group, 5% had LV diastolic abnormality (P = 0.02) and all of them had normal stress test.

Conclusions:

Cardiovascular abnormalities are another late complication in chemical war disabled Iranian victims. Diastolic dysfunction was the most common abnormality in both groups of patients.

Functional and inflammatory alterations in the lung following exposure of rats to nitrogen mustard

Nitrogen mustard is a vesicant that causes damage to the respiratory tract. In these studies, we characterized the acute effects of nitrogen mustard on lung structure, inflammatory mediator expression, and pulmonary function, with the goal of identifying mediators potentially involved in toxicity. Treatment of rats (male Wistar, 200-225 g) with nitrogen mustard (mechlorethamine hydrochloride, i.t., 0.25mg/kg) resulted in marked histological changes in the respiratory tract, including necrotizing bronchiolitis, thickening of alveolar septa, and inflammation which was evident within 24h. This was associated with increases in bronchoalveolar lavage protein and cells, confirming injury to alveolar epithelial regions of the lung. Nitrogen mustard administration also resulted in increased expression of inducible nitric oxide synthase and cyclooxygenase-2, pro-inflammatory proteins implicated in lung injury, in alveolar macrophages and alveolar and bronchial epithelial cells. Expression of connective tissue growth factor and matrix metalloproteinase-9, mediators regulating extracellular matrix turnover was also increased, suggesting that pathways leading to chronic lung disease are initiated early in the pathogenic process. Following nitrogen mustard exposure, alterations in lung mechanics and function were also observed. These included decreases in baseline static compliance, end-tidal volume and airway resistance, and a pronounced loss of methacholine responsiveness in resistance, tissue damping and elastance. Taken together, these data demonstrate that nitrogen mustard induces rapid structural and inflammatory changes in the lung which are associated with altered lung functioning. Understanding the nature of the injury induced by nitrogen mustard and related analogs may aid in the development of efficacious therapies for treatment of pulmonary injury resulting from exposure to vesicants.

Airway hyperresponsiveness to methacholine in chemical warfare victims

BACKGROUND

The lung is one of the most exposable organs to chemical warfare agents such as sulfur mustard gas. Pulmonary complications as a result of this gas range from severe bronchial stenosis to mild or no symptoms. Airway hyperresponsiveness (AHR) which is usually assessed as response to inhaled methacholine is the most characteristic feature of asthma. AHR is reported in chronic obstructive pulmonary disease patients and smokers, and may also show in chemical warfare victims. However, there are little reports regarding AHR in chemical warfare victims.

OBJECTIVE

Therefore, in this study, airway responsiveness to methacholine in victims of chemical warfare was examined.

METHODS

The threshold concentrations of inhaled methacholine required for a 20% change in forced expiratory flow in 1 s (FEV1; PC20) or a 35% change in specific airway conductance (PC35) were measured in 15 chemical war victims and 15 normal control subjects.

RESULTS

In 10 out of 15 chemical warfare victims (two thirds), PC20 and PC35 methacholine could be measured and subjects were called responders. AHR to methacholine in responder chemical war victims (PC20 = 0.41 and PC35 = 0.82 g/l) was significantly lower than in normal subjects (PC20 = 5.69 and PC35 = 4.60 g/l, p < 0.001 for both cases). There was a significant correlation between FEV1 and PC20 methacholine (r = 0.688, p < 0.001). The correlations between PC20 and PC35 were statistically significant as well (r = 0.856, p < 0.001).

CONCLUSION

Results showed increased airway responsiveness of most chemical warfare victims to methacholine which correlated with the FEV1 value and which may be related to chronic airway inflammation or irreversible airway changes.

Myocardial perfusion abnormalities in chemical warfare patients intoxicated with mustard gas

BACKGROUND

Mustard agents are of the major chemical agents used during Iran-Iraq war. There are no reports concerning long-term cardiac effects. The aim was to assess the scintigraphic pattern of myocardial perfusion in patients intoxicated with blistering gases.

METHOD

We analyzed myocardial perfusion scans of 22 consecutive intoxicated patients (21 male and 1 female, all < 44 years) and compared results with 14 controls. Only those patients and controls were entered whose 10-year risk of coronary artery disease (Framingham criteria) was <5%. Also only those patients were experimented upon that had currently other confirmed complications of intoxication (respiratory, cutaneous and ocular complications). All patients underwent a 1-day stress and rest protocol using (99m)Tc-MIBI. Images were assessed visually and quantitatively using Cedars Sinai program.

RESULTS

The prevalence of nonhomogeneity of uptake and left and right ventricular enlargement in both visual and quantitative analyses were higher in the mustard exposed patients than unexposed controls. The prevalence of ischemia was higher in the exposed patients (P < 0.05). Cavity to myocardium ratio, as an established and validated measure of ejection fraction, was also significantly lower in the warfare patients than the controls.

CONCLUSION

In so far it lies in our knowledge, this is the first report concerning the scintigraphic pattern of myocardial perfusion in mustard intoxicated patients. Based on the results, the pattern of myocardial perfusion in these patients is significantly different from normal controls, which could resemble either coronary artery disease or mild cardiomyopathic changes.